1. Field of the Invention
The present invention relates to a battery system that manages individually the degree of power consumption of each battery cell.
Priority is claimed on Japanese Patent Application No. 2009-216956, filed Sep. 18, 2009, the content of which is incorporated herein by reference.
2. Description of Related Art
In general, a control system that controls an assembled battery includes a plurality of CMUs (Cell Monitoring Units) that manages battery cells and a BMU (Battery Management Unit) that manages the operation of the CMUs. Each of the CMUs manages a plurality of battery cells. The CMUs are connected in parallel to the BMU. In recent years, a system has also been proposed which detects the charge state of a plurality of battery cells that is connected in series (for example, see Japanese Laid-Open Patent Publication No. 2003-032907).
However, one CMU can manage a plurality of battery cells at the same time. Therefore, in general, for example, the number of battery cells to be managed by one CMU is set to five in order to reduce the size of the battery system. In this case, the number of battery cells forming the assembled battery needs to be a multiple of five, such as 5, 10, 15, . . . . Therefore, in case of this structure used in the battery system, that uses 12 battery cells as an optimal number of battery cells, the assembled battery needs to be formed by ten battery cells with an insufficient power level, or the assembled battery needs to be formed by fifteen battery cells with wasteful spending. Otherwise, for example, it is necessary to place a special order for a CMU that manages six battery cells.
These battery systems can manage to charge or discharge each battery cell. Therefore, it is also possible to monitor, for example, the temperature and voltage of each battery cell, with the battery cells connected to the CMU and the BMU.
The battery cell is easily replaceable. However, the battery cell prepared for replacement is not always a new battery cell, but it may be a used battery cell. In particular, the battery cell of the secondary battery is rechargeable and can be used for a long time. Therefore, in case of replacing a battery cell in the battery system, a reused battery cell may be prepared for the replacement.
In this case, when the used or reused battery cell is connected to the CMU and the BMU to form the battery system, it is recognized for the first time that the battery cell is the used one or the reused one. When the health of the battery, that is, the power consumption of the battery at that time is not suitable for the use of the battery system, the battery cell is removed from the battery system and is replaced with another battery cell. This is likely to make the maintenance of the battery system complicated. In addition, the battery used for a mobile apparatus, such as an electric vehicle or an industrial vehicle, needs to be higher performance than that of the battery used for a stationary apparatus, such as an emergency power supply for home use. Therefore, it is important to manage the power consumption of the battery cell.